1. Field of the Invention
The present invention relates to a printing apparatus, a printing system, a printing method and a program to print images using a plurality of print heads capable of ejecting ink.
2. Description of the Related Art
Printing very few kinds of materials in large quantities, as in pamphlet printing and corrugated cardboard printing, has conventionally been performed using an offset printing machine and a flexographic printing machine. These printing machines (printing apparatus) require a printing plate for each print job and thus the printing plate must be replaced and ink cleaning done every time the print job is changed. Thus, if these printing machines are used for many-kinds-in-small-lots printing, a unit printing cost increases. Further, inserting a small-lot print job in a large-lot print job in a printing operation using these printing machines will result in a significant fall in efficiency. Further, since the content of printing is fixed by the printing plate, it is impossible to print variable data.
Japanese Patent Application Laid-open No. 2001-331009 discloses a tandem type color printer which prints a color image on a print medium by transferring multicolor toner images formed on a plurality of photosensitive drums onto the print medium. This color printer has a construction for high-speed printing of a single-color image. That is, a toner image of the same color is divided and formed on a plurality of photosensitive drums and these divided toner images are transferred onto the print medium. This method splits the printing operation of a single-color image among the plurality of photosensitive drums.
As the IT technology has advanced in recent years, there is a growing call, as a general trend, for improved services specifically targeted at individual consumers. The printing field is no exception. In a direct mail printing classified in a form printing field, for example, there are increasing needs for variable data printing which prints information (names, addresses, etc.) on destinations (individuals) and advertising information properly focused on the destinations (individuals) in addition to a common information portion. In a corrugated cardboard printing field also, needs are growing for variable data printing which, in addition to printing a common design on all corrugated cardboards, prints manufacturer information (variable data) and serial number for each board in a large-lot printing or small-lot printing run. Further, in an interior material (e.g., wall paper) printing field, there is a growing trend for a small-lot printing that can meet a variety of preferences of end users, rather than printing a single, uniform design.
Against this background, ink jet printing apparatus that require no printing plates and print job changing preparations and which can print variable data are becoming popular.
However, although the ink jet printing apparatus can produce a satisfactory image quality when a print medium is dedicated paper such as coated paper, if such dedicated paper cannot be used, a required level of image quality may not necessarily be obtained.
For example, when an ink jet printing apparatus is employed in the form printing and conventional offset printing paper is used, there is a possibility of the print density becoming insufficient. Further, if the ink jet printing apparatus is employed in a corrugated cardboard printing, since ink dedicated for the ink jet printing apparatus soaks into cardboard quickly, the print density may become undesirably low. In the wall paper printing, although a light tone is desired, it is currently difficult to realize a desired color reproduction capability with the ink jet printing apparatus.
Further, there is available an ink jet printing apparatus of a serial scan type which forms an image by alternately repeating an operation that moves a print head in a main scan direction as it ejects ink and another operation that feeds the print medium in a subscan direction crossing the main scan direction. Some of this type of ink jet printing apparatus employ a multipass printing system that prints a predetermined width of print area on a print medium in a plurality of scans of the print head. This multipass printing system allocates a plurality of pixels on one raster along the main scan direction to a plurality of ink ejection nozzles of the print head so that pixels on one raster are formed by ink droplets ejected from different nozzles. This printing method can suppress adverse effects caused by nozzle variations and thereby print high-quality images. However, as the number of print head scans increases, the printing speed decreases significantly.